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You have a VERY important reason to keep your cover closed at night. There are other advantages too.

I almost always keep my cover closed at night: It helps keep in heat and that has been a real advantage with the cool weather this year! It helps keep critters from finding the pool at night; I never find dead toads, chipmunks, voles, etc. unless I leave it open. If a storm comes up at night, windblown debris stays out. (I rarely have to vacuum because I also close it during the day if there's any type of strong wind).

I leave it open: If my water level is low and it is going to rain with little to no wind. If the pool water temperature gets high and I need to cool it off. If I have to go to shock level. I also left it open while I was lowering my TA and aerating with my fountains.

Good luck with your pool and the party!